Sunset Boulevard. In the studio scene with Cecil B. DeMille, director Billy Wilder intended to feature Hedy Lamarr sitting in her chair (DeMille was filming Samson and Delilah starring Hedy Lamarr). However, Hedy wanted $25,000 for the cameo, so Wilder dropped the idea.
@HannahHowe this is the sort of, "i'm not dong that for free" energy i aspire to.